The invention relates to an interference suppression device for an electric machine, in particular in the form of an electric motor. In addition, the invention relates to an electric motor comprising an interference suppression device according to the invention and to the use of an electric motor.
An interference suppression device is already known in practice. It is part of an electric motor provided with (carbon) brushes in a comfort drive in a motor vehicle and is used for improving or ensuring the electromagnetic compatibility (EMC) of the electric motor. The known interference suppression device in this case comprises two Cy interference suppression capacitors in the case of a 2-pole electric motor, which capacitors are firstly electrically conductively connected to the two power supply lines (carbon brushes) of the electric motor and secondly electrically conductively connected to a ground potential. The interference suppression capacitors are arranged in the region of a brushholder plate consisting of plastics, wherein the wire of the interference suppression capacitor which is used for the connection to ground is arranged such that it is operatively connected to a spring element, which presses the wire against the metal housing (pole pot housing) of the electric motor so as to form a pretensioning force.
It is important for such a connection to ground between an interference suppression element and, for example, the metal housing of the electric motor that, firstly a relatively low contact resistance is achieved and, secondly, a particularly robust and reliable connection which does not change over the operating life of the electric motor is provided.
One disadvantage with the prior art described above consists in that the spring element is fastened to the component part (brushholder plate) only on one side or at one end region, and the level of pretensioning force on the wire of the interference suppression capacitor therefore can only be set or is controllable with relative difficulty. As a result, in particular the mentioned reliable connection to ground of the interference suppression element is not reliably ensured over the life of the electric machine.
Furthermore, further solutions are known from the prior art in which a spring element in the form of a grounding spring is inserted, for example, into a ring-shaped gap between a brushholder plate and the pole pot housing of the electric motor in a manner which is clearly defined, wherein the interference suppression element is connected with its wire to the grounding spring by means of a welded joint. Such a solution is satisfactory in terms of its function, even when considered over the life of the electric motor, but the formation of the welded joint requires increased complexity in terms of installation and manufacturing. A solution is also known in which the interference suppression capacitor is received in clamping fashion with its electrically conductive wire directly between the brushholder body and the pole pot housing. One disadvantage here consists in that owing to the material (plastics) of the brushholder plate which has a relatively high level of elasticity, it is not possible to achieve a clearly defined press-in force, in particular in the case of temperature fluctuations, as result of which the contact resistance can change markedly in the event of temperature fluctuations, with the result that functioning is not ensured.